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Private pilots -- flying one- or two-engine planes -- sometimes make bad decisions up here. They fly through bad weather or fail to consider limitations of their aircraft at higher altitudes.

"Most (crashes) are the result of a pilot who exceeds abilities," said Bob Follett, a pilot for 37 years and owner of Wofford Aviation, a charter service in Fresno.

Still, nobody argues that flying over the Sierra is anything like flying over the flatlands.

Scientists all over the world know about the Sierra's rotor winds -- sideways mini-twisters that can rip apart small planes.

Rotors spin off near the ground, spawned by high-speed spring and fall winds from the west called mountain waves. The waves swoop down the eastern Sierra slope at speeds of up to 100 miles per hour.

This kind of wind occurs in many mountain ranges, but the Sierra's waves are among the most devastating on Earth, scientists said.

"The Sierra's mountain waves are certainly in the top five," said Ronald B. Smith, a Yale University professor of geophysical fluid dynamics who has studied the power of such winds all over the planet.

Vanda Grubisic, an associate research professor at the Desert Research Institute in Reno who has worked with Smith, studies the waves in an effort to make aviation safer. She says trained pilots know the winds are seasonal, occurring mostly in fall and spring.

"They are a true danger for small aircraft," she said. "Summer is a safer time for flying." Mountain waves and rotors are not the only problems. The Sierra is perfectly positioned for radical weather. It is the first substantial barrier encountered by swift global winds from the Pacific Ocean.

Blustery storms smack into the range and flow over peaks; the wind moves just like water flowing and eddying over rocks in a creek bed.

"The wind swirls around those high peaks," said Larry Jobe, a Groveland-based pilot, instructor and member of the Federal Aviation Administration flight safety team. "You're putting yourself at risk if you go up when the wind is blowing 35 mph or greater." Most aviation experts consider mountain waves and other types of wind to be prime culprits in aviation accidents around the world. In the eastern Sierra, there have been dozens of accidents connected to winds, turbulence and downdrafts, according to a survey of National Transportation Safety Board and U.S. military records.

In an accident last year near Independence, in the Owens Valley east of Kings Canyon National Park , the pilot reported that downdrafts from a mountain wave kept his plane from climbing. The plane was forced into a crash landing and had extensive damage, but the pilot survived.

He was fortunate, experts say. He was flying west into the teeth of a mountain wave, which is the worst route to take during the high winds.

Said Yale professor Smith: "Even if you're well-trained, it is very dangerous, very turbulent." The size of this mountain range plays a role in the wind and weather, too.

The Sierra is 400 miles of granite varying in elevation from oak-studded foothills to alpine glaciers. It is the longest contiguous mountain range in the United States, and its vertical reach is equally impressive.

Several hundred peaks are higher than 12,000 feet. The highest is 14,497-foot Mount Whitney, the tallest mountain in the lower 48 states.

At those elevations, snowstorms happen in May and June. Violent thunderstorms blast the crest in summer. Blizzards drop 10 feet of snow in just a few days in winter.

Before air travel, this range was a formidable barrier to transportation. A century ago, the deep snow drifts brought Sierra travel to a standstill.

One of the more famous trans-Sierra routes -- Tioga Road through Yosemite National Park -- still closes every fall when the snow flies.

Now, private air traffic along the range can be busy much of the year. Many flights come from Lake Tahoe, small eastern Sierra airports in Bishop and Mammoth Lakes as well as western slope airports and the rest of the state.

California has more than 30,000 private pilots, more than any other state, according to the national Aircraft Owners and Pilots Association. That's one reason there are so many crashes -- more pilots, more flights, experts said.

Federal authorities have long considered mountain flying more dangerous than flying over flat land. In a 1993 report from the General Accounting Office, officials found the accident rate for private planes was nearly 40 percent higher in mountainous Western states, including California.

Longtime pilot Follett of Fresno gave this scenario to illustrate Sierra dangers: A pilot flies through a mountain pass, but clouds suddenly reduce visibility, forcing the pilot to turn around. The clouds close in all around, the terrain is no longer visible and the pilot panics.

"So they start climbing and fly into clouds and bam, there's a mountain," he said.

Private pilots need to take a mountain flying course, said most safety experts and the FAA. If pilots pay attention to the weather, the capabilities of their aircraft and their training for mountain flying, FAA officials said problems can be minimized.

William Hill, a Redding-based pilot and member of the FAA's flight safety team, said pilots have the same kinds of lapses drivers might have. They may have been well-trained and well-informed about mountains, but they just don't apply what they know.

For instance, there is a big difference between a takeoff from Fresno, near sea level, and a takeoff from Lake Tahoe in thinner air at 6,000 feet elevation, he said.

Because of the higher elevation, the air at Tahoe does not contain as much oxygen as it does in Fresno. The plane's engine -- which needs oxygen to run -- can't produce the same amount of power for takeoff.

Hill said ignoring these limitations is perilous.

"You might need a longer runway to take off and more room to maneuver once you get in the air," he said.

Groveland-based pilot and instructor Jobe, who has been flying almost 50 years, said that the power of nature trumps everything. He told the story of flying a DC-8 commercial flight over the Sierra and being caught in an unexpected and unbelievable updraft.

He said such a wind surge has happened only once in all his years of flying, and there was no damage. But it was unforgettable.

"I'm flying a 300,000-pound plane. In 10 seconds, we climb 1,200 feet on an updraft that came from nowhere. That's how powerful Mother Nature is."